Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

Cant figure this out! Not getting 24v at the board or thermostat

Its a Carrier split unit. Had the heater on yesterday and at some point when I wasnt around it turned off on its on. Its completely dead at the thermostat, and on the circuit board it doesnt get 24 volts either. So I tested voltage going into the transformer and it has 120 volts on all 3 wires going in but it only has .1 volts on the 24v side. Well thats not right. We have a 2 story house and both units have the exact same transformer so I measured the transformer on the working unit to be sure Im dong it right and it measures 120v on all 3 coming in, and about 27 volts going out. So I go and buy a new transformer, wire it up, and still no 24 volts! Did a resistance check, all wires have some resistance. So now Im stumped. If it has voltage coming in, how is it not coming out!? What should I check next?

Winters coming here in n Florida and I finally tackled this problem again, on my own. And I fixed it too! Learned a good bit about the 240 Volts side, contactors, step down transformers. The problem turned out to be a solder point on the control/thermostat board that burned out/shorted out somehow. This solder point fed voltage to M1 (blower motor) and T3 (transformer) That's why I wasn't getting my 240 at the Transformer. Pics are here. I just bypassed the burned up point on the board completely -

< Links to DIY sites are not permitted here. >

Last edited by beenthere; 10-29-2013 at 05:38 AM.
Reason: Removed link to DIY site

So it took you five months to figure out that you had a faulty circuit board, Did you go to hvac school during that time you should have. Just to let you know it usually takes 30 seconds or so to check a board so your doing good. Why didn't you just pay someone to fix it, you know spread the wealth, keep the economy going support local business. not putting your life on the line Priceless. Geez you are cheap.

It's not if your doing it right it's whether your doing the right thing that is important.

That's exactly why. One because Im cheap, and 2 because I love fixing things myself. I didn't work on it for 5 months straight lol. I have a 2 story house and this unit (downstairs) is only used during the winter. I quit working on it the first time (since winter was over) but your right, shouldn't have taken very long to fix. I actually wanted to go to HVAC school but I joined the military instead. They don't pay very good if you haven't heard. I didn't expect anything less from you guys on here as far as comments go lol.

That's exactly why. One because Im cheap, and 2 because I love fixing things myself. I didn't work on it for 5 months straight lol. I have a 2 story house and this unit (downstairs) is only used during the winter. I quit working on it the first time (since winter was over) but your right, shouldn't have taken very long to fix. I actually wanted to go to HVAC school but I joined the military instead. They don't pay very good if you haven't heard. I didn't expect anything less from you guys on here as far as comments go lol.

Yea I did my time and learned a trade while I was at it, Navy- There are more ways too get paid besides monetary compensation, experience the paycheck that keeps giving.

It's not if your doing it right it's whether your doing the right thing that is important.